1. Field of the Invention
The present invention relates to a receiver for receiving a text-based multiplex broadcast.
2. Description of Related Art
In an FM broadcast, for example, within Japan, a transmission referred to as "FM text-based multiplex broadcasting" has been put to practical use for which digital data such as character information is frequency-multiplexed with an original audio broadcast program and transmitted.
This FM text-based multiplex broadcasting system is referred to as the "DARC (Data Radio Channel) system" developed under the leading of the NHK (Nippon Hoso Kyokai: Japan Broadcasting Corporation) Science and Technical Laboratories, and the standard for multiplexing digital data such as character information is:
sub-carrier frequency: 76 kHz PA1 transmission rate: 16 bit/second PA1 modulation system: LMSK (Level controlled Minimum Shift Keying) PA1 error correction method: (272,190) product code with compacted cyclic code of difference set
This LMSK signal is then frequency-multiplexed with an audio signal (monaural signal or stereo composite signal) for the original audio broadcast program and this frequency-multiplexed signal is then transmitted.
Program services such as those of character information are classified into levels 1, 2 and 3, with character information being displayed with dots in all of them. A level 1 program service is, as shown in FIG. 1A, a service for an FM receiver capable of displaying 15.5 characters X 2.5 lines including a header part, with information being given with characters. Further, one text-based program is taken to have a maximum capacity of 62 pages, with one page being made to have 15.5 characters X 2 lines.
News, weather forecasts, traffic information, entertainment and main supplementary programs are considered to be as the level 1 program services. In this case, the entertainment program is to provide information such as fortune telling, listener message boards, quizzes and town information.
The main supplementary program is provided as supplementary information for the original audio broadcast program such as a title of a musical composition, a name of artist, and a telephone and FAX number for the time of making a request when the original audio broadcast program is, for example, a music program. In the following, the main supplementary program is referred to as "program information" or "program linking".
Further, emergency information provided as the occasion calls at times of urgent necessity can also be considered as other program services.
A level 2 program service is a service for FM receivers capable of displaying 15.5 characters X 8.5 lines including the header part where the information is given as characters and figures. Further, a level 3 program service is for FM receivers capable of displaying detailed maps using media such as CD-ROMs, i.e. traffic information services for navigation systems.
[Example of Character Program Display]
An example of character program display as a level 1 program service will be explained with reference to FIG. 1A to FIG. 1H and FIG. 2A to FIG. 2H. In FIG. 2A to FIG. 2H, displays in English correspond to those in Japanese in FIG. 1A to FIG. 1H, respectively.
As shown in FIG. 1A and FIG. 2A, a display element DSP such as an LCD is provided at an FM text-based multiplex broadcast receiver suitable for the level 1 with a display region having a size for 15.5 characters X 2.5 lines (248 dots wide by 40 dots high). The region for the upper half line of this display region is made to be that for a header sentence and the region of the lower two lines is made to be a display region for a body.
When the receiver receives a text-based multiplex broadcast, the first page of the main menu is displayed at the display element as shown in FIG. 1B and FIG. 2B. If a prescribed key is operated when the first page is displayed in this way, the second page of the main menu is displayed as shown in FIG. 1C and FIG. 2C, with other pages of the main menu then being sequentially displayed thereafter in the same manner.
Programs are provided in a hierarchical manner in this main menu so that, for example, when "3. WEATHER FORECAST" is selected from the main menu shown in FIG. 1C and FIG. 2C, the sub-menus "1. WEATHER IN TOKYO AREA" and "2. WEATHER IN KANAGAWA AREA" are displayed as shown in FIG. 1D and FIG. 2D as sub-menus for one order lower programs.
Here, if one who wishes to know the weather for, for example, the Kanagawa area selects "2. WEATHER IN KANAGAWA AREA", then "&lt;KANAGAWA AREA&gt; (TODAY)" is displayed as the first page for the program of a lower hierarchical layer as shown in FIG. 1E and FIG. 2E. If a prescribed key is then pressed in this state, "PROBABILITY OF RAIN" for today in Kanagawa is displayed for the second page as shown in FIG. 1F and FIG. 2F. If a prescribed key is then pressed by turns as necessary, "&lt;KANAGAWA AREA&gt; (TOMORROW)" for the third page shown in FIG. 1G and FIG. 2G and "PROBABILITY OF RAIN" for tomorrow in Kanagawa of the fourth page shown in FIG. 1H and FIG. 2H are displayed.
Since the main menu has the programs and sub-menus that are thus provided in a hierarchical manner, the desired text-based program can be displayed by following them in order.
When data for a text-based program is received in the above described FM text-based multiplex broadcast receiver, all of the valid data is temporarily stored at a memory for a reception buffer, with the required data being read out from the saved data and the desired character data then being displayed.
Usually, data in memory is erased when the power supply is turned off, but in this case, if it is ensured that the data stored in memory is made to remain even if the power supply is turned off, thereby the data can be effectively utilized. For example, weather forecasts and traffic information can be confirmed even after the power supply is turned off.
However, if the data saved in memory in this way is turned to remain even when the power supply is made off, a problem will occur as to the time of erasing this data. Namely, the data in memory is erased by following two methods.
(1) The data is erased when, for example, 10 minutes have passed from the power supply being off. Alternatively, when the power supply is turned on after more than ten minutes have passed, this data is erased at the time of turning the power on.
(2) If new data can be received, the new data is overwritten on the old data without particularly erasing the old data when the power supply is turned on and off.
However, in the method in item (1), as there are differences in the perception of the users with respect to the data save time (the time from the power supply being turned off to the erasure of data being valid. In the above case this is 10 minutes), this cannot be said to be the most suitable method. Further, since the valid period for the data is different with, for example, general news and traffic information, the fixed save time can be meaningless.
Further, in method (2), the program being watched is old one in the period until the newest data is taken in, so that if the user mistakes this for the newest program without noticing, this information is, in a sense, incorrect. In addition, when another broadcast station is selected, the text-based program for the broadcast station having been selected before has been unconditionally erased, so that when a broadcast station for the program that one wishes to listen to is different from that for the text-based program that one wishes to watch, both wishes cannot be satisfied.